See this:

http://www.google.com/search?hl=en&s... aq=f&oq=&aqi=

--
Biff
Microsoft Excel MVP


"rojobrown" wrote in message
...
I have the following formula that is used to calculate a MOD 10 check digit
routine. For example: If I entered (8 digits) 45678912 in cell A1, the
formula would return a 2 as the 9th digit.

This is the formula that I am using but did not write so I'm having
trouble
following it.
=10-MOD(SUM(--MID(TEXT($A1,"000000000"),{2,4,6,8},1),--RIGHT(MID(TEXT($A1,"000000000"),{1,3,5,7,9},1)*2),--LEFT(TEXT((MID(TEXT($A1,"000000000"),{1,3,5,7,9},1 )*2),"00"))),10)

I need to modify this formula so that it will look at 15 digits and
calculate the 16th. I've tried multiple things but have had no luck. Any
suggestions?